The invention relates to monitoring the head-disk interface for disk drives and more particularly concerns the ramp load/unload testing of the magnetic head slider, disk and ramp.
Disk drives, also referred to as hard disk drives and direct access storage devices, have one or more disks on the surface of which is a thin magnetisable layer. Information is written to and read from the disks using one or more read and/or write heads attached to a slider. The slider is supported on a head gimbal assembly (HGA).
When the disk drive is in operation, the disks are quickly rotating and the slider is spaced from the disk surface by an air-bearing effect due to the disks"" rotation. When the disk drive is not in operation, the slider can be parked or brought to rest according to one of two methods. The first method is to rest the slider directly on the disk surface. This method is referred as a contact start/stop (CSS). The second method is to park the HGA on a ramp provided adjacent the perimeter of the disk in order to keep the slider spaced from the disk surface. This method is referred to as a dynamic load/unload (L/UL).
In disk drives that use the CSS method of parking the slider, when the disk drive is turned off the slider rests on the disk surface. When the disk drive is powered on for operation the slider takes off from the disk surface because of the air-bearing effects induced by the disk rotating. One concern with the CSS method of parking the slider is that stiction (static friction) between the slider and disk surface when the disk drive is powered on results in wear on the disk surface, ultimately producing errors. Further, during manufacture of a disk drive using the CSS method of parking the slider, the head stack assembly (HSA) composed of two or more head gimbal assemblies needs to be loaded to the disk surfaces. This loading operation may also cause damage to the disk surfaces and/or the sliders.
In disk drives utilizing the L/UL method of parking the slider, a parking ramp forms part of the disk drive and is located adjacent to the disk surface. When the disk drive is powered off, the HSA is rotated to a parked position in which a portion of each HGA, called the ramp rider or the lift tab, rests on the ramp above the disk surface. In this state, the slider is spaced from the disk surface. When the disk drive is powered on, the HSA is moved from the parked position off the ramp to place the slider above the disk surface.
Each HGA includes a suspension member that is mounted to an actuator assembly. The suspension member carries the slider at its free end and biases the slider against the disk surface. When the disk rotates, the air-bearing creates a lifting force that counter-balances the bias of the suspension member. When the disk drive is powered off and the ramp rider is parked on the ramp, the suspension member continues to exert a force on the ramp directed toward the disk surface. Under prolonged contact, the loading force from the suspension member contributes to stiction between the ramp rider and the ramp. This stiction can hinder the loading and unloading operation.
Further, during a loading operation, when the HGA is moved from the parked position to the disk surface, the stiction forces can exceed the torque available to move the actuator assembly to which the suspension is coupled. This results in failure of the disk drive.
During a load/unload operation when the HGA is moved from/to the ramp, there is an opportunity for slider disk surface contact to occur which can result in a so-called head crash.
The HGA and the disk are typically tested before being confirmed as components of a hard disk drive. For a CSS tester, the only concern is the slider-disk interaction. For a L/UL tester, there are two concerns: the slider-disk interaction and the HGA-ramp interaction.
Prior L/UL testers include force sensors that measure the friction force between the slider and the disk and an acoustic emission (AE) sensor to monitor the slider-disk interaction. Such L/UL testers can not be used to monitor the entire load/unload process. Accordingly, there is a need for a new load/unload tester that can be used to monitor HGA-ramp interaction and the slider-disk interaction at the same time.
In accordance with a first aspect of this invention, there is provided an apparatus for monitoring a load/unload process in a disk, a ramp and a head-gimbal-assembly (HGA), comprising:
a ramp strain arm comprising a deformable member and force sensing means provided on said deformable member, said ramp being mounted on said deformable member;
an actuator assembly, the HGA being mounted on the actuator assembly, the actuator assembly controlling movement of the HGA to and from a loaded position on the ramp; and
control means in communication with the force sensing means to receive signals therefrom representative of the force on the ramp from the HGA.
Preferably, said force sensing means comprises first force sensors arranged to measure the friction force between the HGA, and the ramp, and second force sensors arranged to measure the force which acts on the ramp along a direction perpendicular to the disk""s surface.
Preferably, said force sensing means comprises force sensors arranged to measure the friction force between the HGA and the ramp.
Preferably, said force sensing means comprises force sensors arranged to measure the force which acts on the ramp along a direction perpendicular to the disk""s surface.
Preferably, the force sensing means further comprises an AE sensor arranged to monitor the interaction between the HGA, the disk and the ramp.
Preferably, said control means is arranged to control operation of a motor that revolves the disk.
Preferably, said control means is arranged to control operation of the actuator assembly for moving the HGA.
In accordance with a second aspect of this invention, there is provided an apparatus for monitoring a load/unload process in at least one disk, a plurality of ramps and a head-stack-assembly comprising a plurality of head-gimbal-assemblies (HGAs), comprising:
a plurality of ramp strain arms, each comprising a deformable member and force sensing means provided on said deformable member, each ramp strain arm having a ramp mounted on its deformable member;
an actuator assembly, the HSA being mounted on the actuator assembly, the actuator assembly controlling movement of the HGAs to and from a loaded position on the ramps; and
control means in communication with the force sensing means to receive signals therefrom representative of the force on the corresponding ramp from the corresponding HGA.
Preferably, said force sensing means of each ramp strain arm comprises first force sensors arranged to measure the friction force between the corresponding HGA and the corresponding ramp, and second force sensors arranged to measure the force which acts on the corresponding ramp along a direction perpendicular to the disk""s surface.
Preferably, said force sensing means of each ramp strain arm comprises force sensors arranged to measure the friction force between the corresponding HGA and the corresponding ramp.
Preferably, said force sensing means of each ramp strain arm comprises force sensors arranged to measure the force which acts on the corresponding ramp along a direction perpendicular to the disk""s surface.
Preferably, the force sensing means further comprises an AE sensor arranged to monitor the interaction between the corresponding HGA, the disk and the corresponding ramp.
Preferably, said control means is arranged to control operation of a motor that revolves the disk.
Preferably, said control means is arranged to control operation of the actuator assembly for moving the HGA.
In accordance with a third aspect of this invention, there is provided a ramp strain arm for monitoring a load/unload process in a disk, a ramp and a head-gimbal-assembly (HGA), comprising a deformable member and force sensing means provided on said deformable member, said ramp being mounted on said deformable member; whereby said force sensing means produce signals representative of the force on the ramp from the HGA.
Preferably, said force sensing means comprises first force sensors arranged to measure the friction force between the HGA and the ramp, and second force sensors arranged to measure the force which acts on the ramp along a direction perpendicular to the disk""s surface.
Preferably, said force sensing means comprises force sensors arranged to measure the friction force between the HGA and the ramp.
Preferably, said force sensing means of comprises force sensors arranged to measure the force which acts on the ramp along a direction perpendicular to the disk""s surface.
Preferably, the force sensing means further comprises an AE sensor arranged to monitor the interaction between the HGA, the disk and the ramp.
Preferably, the force sensors comprise strain gauges.
Preferably, the force sensors comprise piezo-electrical strain sensor.
In accordance with a fourth aspect of this invention, there is provided a method for monitoring the performance and/or the load/unload process of the combination of a HGA, disk and ramp comprising the steps of:
providing means for supporting said disk for rotation about a central axis extending perpendicular to the substrate plane of disk;
providing a head-disk assembly comprising a slider carrying a read/write element and having an air-bearing surface, suspension and ramp rider;
providing a ramp strain arm having a deformable member and force sensors provided on said deformable member;
mounting the ramp on the deformable member; and
recording signals from the force sensors.
Preferably, the method further comprises the steps of:
providing a HGA strain arm comprising a deformable member, force sensors provided on said deformable member and an AE sensor;
mounting said HGA on said deformable member; and
recording signals from the force sensors and the AE sensor.